The invention relates to valves used to throttle inlet flow of a liquid to a pump, typically a high-pressure pump used to supply high-pressure fluid to pressure-operated components of an internal combustion engine and to related methods.
Diesel engines using Hydraulic Electronic Unit Injector (HEUI) systems are well known. In these systems, low-pressure liquid, typically engine oil, is pumped to a high-pressure and used to operate electronically actuated fuel injectors. Similar hydraulic systems may be used to supply high-pressure fluid to operate electronically actuated intake and exhaust valves.
U.S. Pat. No. 6,390,072 discloses a HEUI system for a diesel engine using a high-pressure pump and a hydraulic circuit including an inlet throttle valve for throttling the flow of low-pressure engine oil to the inlet of the high-pressure pump. The inlet throttle valve is controlled in response to an injection pressure regulator (IPR) valve which supplies a hydraulic signal to the inlet throttle valve proportional to the difference between the desired output pressure of the high-pressure pump and the actual output pressure of the pump. In this system, engine oil is supplied to the inlet throttle valve from the low-pressure engine pump used to supply engine oil to bearings and cooling jets. The oil is flowed from the inlet throttle valve to the high-pressure pump. The high-pressure pump and hydraulic control system for the pump work well and represent a marked improvement over prior systems. Nonetheless, testing of the hydraulic circuit and inlet throttle valve indicates an opportunity exists to improve performance of the circuit.
The circuit can be improved during low speed or idling operation of the engine to reduce modulation of the inlet throttle valve. This modulation is believed to occur because the pressure of oil supplied to the inlet throttle valve changes significantly for different operating conditions of the engine. Oil from the low-pressure pump acts directly on one side of the inlet throttle valve spool biasing the spool in an opening direction. Variations in the bias force adversely affect stability of the system. Thus, there is a need for an improved inlet throttle valve for stable operation during low speed operation of the engine.
When a diesel engine using the prior hydraulic control system is operated at a high engine speed, and the IPR valve generates a signal to rapidly reduce output pressure a resultant rapid pressure increase in the hydraulic circuit may affect the stability of the system. The instability is believed to result from a rise in pilot pressure when the inlet throttle spool reaches the end of its travel and engages a stop. Thus, there is a need for an improved inlet throttle valve for dumping increased bleed flow to the sump.
Further, there is a need for an inlet throttle valve and control system for a high-pressure pump where the inlet throttle valve has improved rapid response to control signals.
In the conventional hydraulic control, movement of the inlet throttle spool to the closed position is limited by surface-to-surface engagement between the spool and a fixed stop surface. This engagement is believed undesirable because of possible mechanical injury to the spool at the point of engagement and because the mechanical stop occurs abruptly and may destabilize the spool.
In many internal combustion engines it is desirable to bring the engine to operating temperature rapidly and reduce combustion pollutants. Accordingly, there is a need for an improved inlet throttle valve which, at start up, is maintained in an open position to permit high flow of oil to the high-pressure pump so that energy of excess flow from the high-pressure pump is converted to heat and warms the engine.
The invention is an improved inlet throttle valve and method. The valve has a lightweight spool that is rapidly responsive to input signals. The valve includes a passage leading to the sump that is opened when the spool is moved to the closed position to direct increased bleed signal flow to the sump without disrupting operation of the IPR valve. The inlet throttle valve has a hydraulic stop limiting movement of the spool toward the closed position without mechanical engagement between the spool and a stop member.
At startup of the engine, the inlet throttle valve automatically holds the inlet throttle valve spool in a fully open start position for a period of time so that oil supplied to the inlet throttle valve from the low-pressure pump is flowed to the inlet of the high-pressure pump through a large area flow opening, substantially without obstruction. More oil is pumped by the high-pressure pump than is required to drive the injectors. Excess pressurized pump flow is throttled by valve and is returned to the sump. Since no work is being done by the oil, the temperature of the oil rises to warm the engine. This facilitates rapid warm up of the engine.
After a selected period of time, the spool automatically moves from the start up position to an open operating position to reduce the large flow opening and is in position to throttle flow to the high-pressure pump throughout its operating range, responsive to input signals from the IPR valve. During the startup period, the spool does not respond to signals received from the IPR valve.
Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention.